1. Field of the Invention
The present invention relates to a method for simulating an impurity diffusion in a semiconductor while the semiconductor is being oxidized.
2. Description of the Related Art
In a prior art method for simulating a concentration of impurities within a silicon material while the silicon material is being oxidized, first mesh points are set in a silicon oxide (SiO.sub.2) region of the silicon material and second mesh points are set in a silicon (Si) region of the silicon material. Then, an old SiO.sub.2 /Si interface is advanced in said semiconductor material by a first distance determined by performing an oxidation operation upon the silicon material for a unit time period, so that a new SiO.sub.2 /Si interface is set in the semiconductor material. Then, the old SiO.sub.2 /Si interface is retarded by a second distance corresponding to a volume expansion of the semiconductor material determined by performing the oxidation operation upon the silicon material for the unit time period. In addition, an impurity transport flux by the motion of the SiO.sub.2 /Si interface is introduced, so that the effect of the impurity segregation at the SiO.sub.2 /Si interface can extend over a region where silicon oxide grows, thus enhancing the transport of impurities within this region. Thus, concentrations of impurities for the first mesh points are obtained by solving a first diffusion equation using a first impurity diffusion coefficient effective in SiO.sub.2 and the impurity transport flux by the motion of the SiO.sub.2 /Si interface, and concentrations of impurities for the second mesh points are obtained by solving a second diffusion equation using a second impurity diffusion coefficient effective in Si. This will be explained later in detail (see D. A. Antoniadis et al., "Impurity Redistribution in SiO.sub.2 -Si during Oxidation: A Numerical Solution Including Interfacial Fluxes", Journal of the Electrochemical Society, Vol. 126, No. 11, pp. 1939-1945).
In the above-described prior art impurity diffusion simulation method, however, since the impurity transport flux by the motion of the SiO.sub.2 /Si interface is defined only between a mesh point at the new SiO.sub.2 /Si interface and another mesh point within SiO.sub.2 adjacent to this mesh point, the distance between the old SiO.sub.2 /Si interface and the new SiO.sub.2 /Si interface determined by the time period is limited, since no additional mesh point is set between the old SiO.sub.2 /Si interface and the new SiO.sub.2 /Si interface. In addition, the above-described prior art impurity diffusion simulation method cannot be applied to a two-dimensional or three-dimensional impurity diffusion case.